If the AI goal is the protection of humans, will it always pursue this goal?
If the main goal of AI (which I assume you mean an AGI) is to protect humans and AI will be effective, then AI will always attempt to pursue its main goal (otherwise the assumption of its effectiveness does not hold), even at the expense of other less important goals that it might have. However, if the destruction of a human (or a group of humans) protected or avoided the destruction of other humans, then AI would face a dilemma. In that case, I think it is hard to predict the actions of the AI. Will it act rationally or irrationally? What would it mean for the AI to act rationally? Which parameters will it take into account? Only the number of deaths, or will take into account the future and weight the importance of the lives? How will it define the importance of a human life?